The combined effects of cervical electrical stimulation alone or in combination with the monoaminergic agonist buspirone on upper limb motor function were determined in six subjects with motor complete (AIS B) injury at C5 or above and more than one year from time of injury. Voluntary upper limb function was evaluated through measures of controlled hand contraction, handgrip force production, dexterity measures, and validated clinical assessment batteries. Repeated measure analysis of variance was used to evaluate functional metrics, EMG amplitude, and changes in mean grip strength. In aggregate, mean hand strength increased by greater than 300% with transcutaneous electrical stimulation and buspirone while a corresponding clinically significant improvement was observed in upper extremity motor scores and the action research arm test. Some functional improvements persisted for an extended period after the study interventions were discontinued. We demonstrate that, with these novel interventions, cervical spinal circuitry can be neuromodulated to improve volitional control of hand function in tetraplegic subjects. The potential impact of these findings on individuals with upper limb paralysis could be dramatic functionally, psychologically, and economically.

The translational linear vestibuloocular reflex compensates most accurately for high frequencies of head translation, with response magnitude decreasing with declining stimulus frequency. However, studies of the perception of translation typically report robust responses even at low frequencies or during prolonged motion. This inconsistency may reflect the incorporation of nondirectional sensory information associated with the vibration and noise that typically accompany translation, into motion perception. We investigated the perception of passive translation in humans while dissociating nondirectional cues from actual head motion. In a cue-dissociation experiment, interaural (IA) motion was generated using either a linear sled, the mechanics of which generated noise and vibration cues that were correlated with the motion profile, or a multiaxis technique that dissociated these cues from actual motion. In a trajectory-shift experiment, IA motion was interrupted by a sudden change in direction (+/-30 degrees diagonal) that produced a change in linear acceleration while maintaining sled speed and therefore mechanical (nondirectional) cues. During multi-axis cue-dissociation trials, subjects reported erroneous translation perceptions that strongly reflected the pattern of nondirectional cues, as opposed to nearly veridical percepts when motion and nondirectional cues coincided. During trajectory-shift trials, subjects' percepts were initially accurate, but erroneous following the direction change. Results suggest that nondirectional cues strongly influence the perception of linear motion, while the utility of cues directly related to translational acceleration is limited. One key implication is that "path integration" likely involves complex mechanisms that depend on nondirectional and contextual self-motion cues in support of limited and transient otolith-dependent acceleration input.

BACKGROUND: Deep brain stimulation (DBS) is a highly efficacious treatment for appropriately selected patients with advanced, medically refractory Parkinson's disease (PD). It is severely underutilized in Black patients-constituting a major treatment gap. The source of this disparity is unknown, but its identification and correction are necessary to provide equitable care. OBJECTIVE: To identify sources of racial disparity in DBS for PD. METHODS:We predicted the demographics of potential DBS candidates by synthesizing published data on PD and race. We retrospectively examined the clinical course of a cohort including all patients with PD evaluated for DBS at our center from 2016 to 2020, testing whether the rate of DBS use and time from evaluation to surgery differed by race. We also tested whether the geographic distribution of patient catchment was biased relative to racial demographics. RESULTS: Far fewer Black patients were evaluated for DBS than would be expected, given regional demographics. There was no significant difference in the rate at which Black patients evaluated in our clinic were treated with DBS, compared with White patients. Fewer patients were recruited from portions of the surrounding area with larger Black populations. CONCLUSION: The known underuse of DBS in Black patients with PD was replicated in this sample from a center in a racially diverse metropolitan area, but was not attributable to the presurgical workup. Future work should examine the transition from medical management to surgical evaluation where drivers of disparity are potentially situated. Surgical practices should increase outreach to physicians managing PD in underserved areas.

Millions of people worldwide are afflicted with paralysis from a disruption of neural pathways between the brain and the muscles. Because their cortical architecture is often preserved, these patients are able to plan movements despite an inability to execute them. In such people, brain machine interfaces have great potential to restore lost function through neuroprosthetic devices, circumventing dysfunctional corticospinal circuitry. These devices have typically derived control signals from the motor cortex (M1) which provides information highly correlated with desired movement trajectories. However, sensorimotor control simultaneously engages multiple cognitive processes such as intent, state estimation, decision making, and the integration of multisensory feedback. As such, cortical association regions upstream of M1 such as the posterior parietal cortex (PPC) that are involved in higher order behaviors such as planning and learning, rather than in encoding movement itself, may enable enhanced, cognitive control of neuroprosthetics, termed cognitive neural prosthetics (CNPs). We illustrate in this review, through a small sampling, the cognitive functions encoded in the PPC and discuss their neural representation in the context of their relevance to motor neuroprosthetics. We aim to highlight through examples a role for cortical signals from the PPC in developing CNPs, and to inspire future avenues for exploration in their research and development.